I've just got a 3year old yorkshire terrier and she's stopped eating can you help me

If she has been a good eater, and suddenly quit, she is sick. You can wait and hope for the best, but really should take her to the vet.

If she has been a picky eater all along and now isn't eating at all, likely she is over fed. Check her as this link shows, http://www.puppychow.com/products/popup_body_condition.aspx If she is too fat, put her on this regimen until she has a waist:

Put down the dish with what the dog should eat, and give it 15 minutes to eat. Then take it up. Do not give it anything to eat until its next scheduled meal. In a few days, it should be eating what it needs. Continue to check its ribs and adjust the food as needed. This is not easy. I had a Shepherd go 3 days on a few nibbles. I was a wreck, but she was fine. It is almost unknown for a healthy dog not to eat what it needs. Unfortunately, in too many cases, it is less than the package says, and less than the owner thinks the dog should have. Many dogs are quite good at holding out for tastier chow. Like kids, sometimes it calls for tough love.

How long have you had her? Many times dogs will stop eatting when entering a new home. While it is a good thing that she is with you, it is still stressful. Try tempting her with some plain lean pieces of chicken breast. Not too much and get her on a good quality food.